1. Field of the Invention
The present invention relates to an automatic exposure control apparatus for an image sensor employed by a camera module and a method thereof, and more particularly, to an automatic exposure control apparatus for an image sensor, the apparatus controlling an exposure to be suitable by using average brightness and changing a shutter speed by using a digital filter, thereby actively and quickly adapting to rapid and frequent brightness variances.
2. Description of the Related Art
In general, in the case of general cameras, automatic exposure control of suitably controlling brightness of inputted images is performed. The automatic exposure control is performed by controlling an aperture ratio of an aperture and controlling a speed of a shutter.
On the other hand, in the case of general digital cameras, solid imaging devices such as charged coupled devices (CCDs) and complementary metal-oxide semiconductors (CMOSs) are used as an image sensor, in which an amount of exposure is controlled by controlling a time for being photographed by the image sensor. In this case, the time for being photographed by the image sensor corresponds to a speed of an electronic shutter. Brightness of an image is controlled to be suitable by changing the speed of the electronic shutter.
FIG. 1 is a block diagram illustrating an image sensor of a conventional digital camera.
The image sensor shown in FIG. 1 includes a lens unit 10 receiving an incident image, an image sensing unit 20 having a shutter, photographing an image from the lens unit 10 via the shutter, and converting into an electric image signal, an image signal processing unit 20 restoring the image signal from the image sensing unit 20 to the image, and a micro controller 40 calculating brightness of the image signal from the image signal processing unit 30 and controlling the shutter of the image sensing unit 20 according to a difference between the calculated brightness and reference brightness.
An exposure control process in the micro controller 40 will be described as follows.
The micro controller 40 calculates brightness of a present image for each frame (S41), calculates a difference between the calculated brightness and reference brightness (S42), calculates a brightness adjustment value according to the difference of brightness (S43), obtains a future application value by adding the adjustment value to a present exposure conversion value (S44), obtains an approximate multiple value by approximating the future application value to a multiple of the least exposure time (S45), and controls the shutter of the image sensing unit 20 by using the multiple (S46).
However, in the case of the exposure control method of the conventional digital camera, when there is a rapid change in exposure of an input image while performing a calculation for obtaining a suitable exposure by using an exclusive micro controller, a large amount of time is required to obtain the suitable exposure.
Also, in a process of calculating based on information on brightness of an image signal, since data on the brightness is excessively large, a large amount of time is required to calculate.
In addition, when an exposure rapidly and frequently changes for a short time, since the micro controller is not capable of recognizing a rapid exposure change, brightness cannot be controlled to be suitable when there is the rapid exposure change.